The design of solar cells that employ light-harvesting rods sandwiched between an electrode and a counterelectrode has been described. The rods are attached to the electrode and are in communication with the counterelectrode. The latter communication is via either a diffusive agent or by direct contact of the rod. The pigments in the rod absorb light and funnel excited-state energy to one end, whereupon electron injection into the electrode occurs. The resulting ground-state hole then flows toward the other end of the rod (See, e.g., U.S. Pat. No. 6,420,648 to Lindsey; U.S. Pat. No. 6,407,330 to Lindsey and Meyer; Loewe, R. S. et al., J. Mater. Chem. 2002, 12, 1530-1552). In this manner, the rod acts as a photodiode, causing rectification of the flow of excited-state energy and ground-state holes.
The fabrication of this type of molecular-based solar cell presents a number of challenges, including the synthesis of light-harvesting rods, the attachment of the rods to a surface, and the attachment of the counterelectrode to complete the sandwich architecture. We have recently described the synthesis of light-harvesting rods that are reasonably long (10-30 units), provide good coverage over much of the solar spectrum, and are soluble in organic solvents thereby enabling solution processing (Loewe, R. S. et al., J. Mater. Chem. 2002, 12, 3438-3451). One challenge that is faced in the solution synthesis approach is that the rods must be soluble in organic solvents for purification and processing. A second challenge is that the rods must be attached to the electrode surface with high surface coverage. Accordingly, there remains a need for new ways to manufacture such solar cells.